The control of pituitary secretion of growth hormone (GH) secretion is mediated by a complicated feedback system involving growth hormone- releasing hormone (GHRH) and somatostatin (SRIF) secretion from the hypothalamus, GH released from the anterior pituitary and locally produced and/or cirulating insulin-like growth factor I (IGF-I). The major aim of this investigation is to determine (a) if and how systemic IGF-I regulates GH secretion in normal men and women. In addition, we will (b) determine if IGF-I has a similar regulatory role in GH secretion in acromegaly and we will (c) investigate how the pattern of GH secretion changes in women during the menstrual cycle.